I found a couple of problems running HAP-Q. I don't know if they are bugs in the HAP codec or in the Isadora's player.

1\. If I run two players with the same file, but different play regions, only first player works as expected, the other one's play head is stuck. I found a way to unstuck it: change the performance to interactive or vice versa on entering the scene.

2\. One of the HAP-Q files stopped playing full length at some point, with no changes in Isadora patch: it would play only a few frames.

Although there is a directshow extension available from a 3rd party vendor, DirectShow playback has not been extended to support this extension.
The only way to play HAP with gpu acceleration is as QuickTime.

The DirectShow settings allow you to natively play 'wmv' among others.

I really don't know why you would get better performance with Hap encoded avi's playing via quicktime.
May simply be defaulting to something like pjpeg and have a smaller file size.